There are many different types of electrical micro-relay devices, and one popular type is the reed micro-relay, which is a small, mechanical contact type of electrical micro-relay device. A reed micro-relay has two reeds made of a magnetic alloy sealed in an inert gas inside a glass vessel surrounded by an electromagnetic driver coil. When current is not flowing in the coil, the tips of the reeds are biased to break contact and the device is switched off. When current is flowing in the coil, the tips of the reeds attract each other to make contact and the device is switched on.
The reed micro-relay has problems related to its large size and relatively short service life. As to the first problem, the reeds not only require a relatively large space, but also do not perform well during high frequency switching due to their size and electromagnetic response. As to the second problem, the flexing of the reeds due to biasing and attraction causes mechanical fatigue, which can lead to breakage of the reeds after extended use.
In the past, the reeds were tipped with contacts composed of rhodium (Rh) or tungsten (W), or were plated with rhodium (Rh) or gold (Au) for conductivity and electrical arcing resistance when making and breaking contact between the reeds. However, these contacts would fail over time. This problem with the contacts has been improved with one type of reed micro-relay called a xe2x80x9cwetxe2x80x9d relay. In a wet relay, a liquid metal such as mercury (Hg) is used to make the contact. This solved the problem of contact failure, but the problem of mechanical fatigue of the reeds remained unsolved.
In an effort to solve these problems, electrical micro-relay devices have been proposed that make use of the liquid metal in a channel between two micro-relay electrodes without the use of reeds. In the liquid metal devices, the liquid metal acts as the contact connecting the two micro-relay electrodes when the device is switched ON. The liquid metal is separated between the two micro-relay electrodes by a fluid non-conductor when the device is switched OFF. The fluid non-conductor is generally high-purity nitrogen or some other such inert gas.
With regard to the size problem, the liquid metal devices afford a reduction in the size of an electrical micro-relay device since reeds are not required. Also, the use of the liquid metal affords longer service life and higher reliability.
The liquid metal devices are generally manufactured by joining together two substrates with a heater in between to heat the gas. The gas expands to separate the liquid metal to open and close a circuit. Previously, the heaters were inline resistors patterned directly on the surface of one of the substrates. The substrates were of materials such as glass, quartz, and gallium arsenide upon which the heater layer was deposited and etched. Since only isotropic etching could be used, the heater element would consist of surface wiring. The major drawback of surface wiring would be loss of heat due to thermal transfer into the underlying substrate.
More recently, suspended heaters have been developed. A suspended heater refers to a configuration in which the heating elements are positioned with a portion directly supported by the silicon substrate and the remaining portion supported over an opening so that the remaining portion can be completely surrounded by the gas.
Problems with previous suspended heaters included the difficulty of handling the power required for heating at smaller sizes.
Further, where heating elements have portions directly supported by silicon substrates, there is a relatively large amount of thermal loss, which must be offset by higher power being applied to the heating elements. This in turn can result in lower reliability.
Solutions to these problems have been long sought, but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.
The present invention provides a switch device and method for manufacturing the switch device in which substrates are provided collectively having defined therein a liquid metal switch and a sub-channel connected to the liquid metal switch. A cavity filled with sacrificial material is formed in a first one of the substrates. A heater element is formed at least in part over the sacrificial material and conductive vias are formed extending through one of the substrates to the heater element. The sacrificial material is removed and the substrates are joined with an adhesive seal.
Certain embodiments of the invention have other advantages in addition to or in place of those mentioned above. The advantages will become apparent from a reading of the following detailed description when taken with reference to the accompanying drawings.